This invention relates generally to antennas and more specifically to a new and improved array, particularly to a planar log periodic quad array.
Log periodic dipole arrays (LPDA's), including the hybrid log periodic yagi (LPY) are well known to radio amateurs. Perhaps less well known to radio amateurs are log periodic quad arrays (LPQA's).
The basic theory of a conventional log periodic array (LPA) is that the array is balanced with elements on one bay offset by equally long opposing elements on the opposite bay and with the two bays being fed 180.degree. out of phase through single conductor feed line booms. The log periodic arrangement of the elements provides a uniform gain over a wide frequency range by progressively scaling down the spacing distance between adjacent elements by a constant multiplier, such as 0.9 for example. Because the two bays aim forward as opposed to being in the same plane the array has a front-to-back ratio in the direction of the smaller elements.
An LPDA can be derived from the basic LPA if the two bays are moved together and the booms made very close or in fact replaced by a two wire balanced transmission line twisted between each set of elements. The LPDA has a gain in the direction of the smaller elements also giving it a front-to-back ratio.
An LPQA can be derived from an LPDA by replacing each dipole with a loop (quad element) resonant at the same frequency. While a full wave loop has several db gain over a dipole it would seem that such an LPQA should have an improvement over the LPDA. It has been found however that while such an antenna may perform well over a limited frequency range it has other deficiencies that can be identified through application of either quad or log periodic theory. For example, at most one loop is exactly a full wave with the others being progressively larger or smaller. The resultant current maxima in the other loops are not distributed in a symmetrical manner about a single central plane, the current patterns do not contribute efficiently toward a single pattern of forward gain, and the resistance and reactance patterns at the feed point may show significant excursions.
An improved form of LPQA is disclosed in U.S. Pat. No. 3,273,159.
The present invention is an outgrowth of attempts to further improve upon an LPQA and it results in an array having particular advantages over other arrays. Moreover, it has the potential for use as either an active or passive part of an antenna. When operating actively it provides a bi-directional pattern characterized by gain over a dipole.
Moreover it has a broadband capability which makes it especially well suited for use with expanded frequency ranges which have recently been authorized by the Federal Communications Commission for amateur radio usage. Although amateur radio usage is one application of the invention, principles of the invention may be more broadly applied.
For example when the array is used as a passive part in a larger antenna it can be used to modify or enhance the basic characteristics of the antenna, for example by imparting particular directional characteristics to the antenna. When used as an active element, an array embodying principles of the invention offers gain over a conventional dipole and it also affords broadband coverage with a single feed line. Various embodiments of the invention may use various scaling factors for the log periodic aspect, for example a range of log periodic scaling from 0.7 to 0.9 is a typical range with in which a particular scaling factor for any given array may be selected.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.